After a CCN instance is created, the system will automatically create a route table and control route entries to manage traffic on CCN. You cannot manually add or delete routes, but you can enable or disable them.

Automatic Route Addition

The logic of automatic route addition in CCN involves three stages as shown below:

1. Before addition: logic for receiving routes, i.e., determining which routes can be added to the CCN route table.
2. During addition: logic for route to take effect by default, i.e., determining which routes added to CCN can take effect.
3. After addition: logic for setting route priority, i.e., determining which effective routes will forward traffic.

1. Before addition

• The associated instance is a VPC in public cloud: for a new subnet, the destination is a subnet IP range, and the next hop is VPC route to CCN.
• The associated instance is a Direct Connect gateway: the destination is an IDC IP range, and the next hop is Direct Connect gateway route to CCN. There are two ways to pass the route:
  i. Manual entry (static): you need to manually enter the IDC IP range to be passed to CCN, and the next hop is the corresponding Direct Connect gateway, which facilitates IP range convergence and filtering.
  ii. Dynamic learning (BGP): this refers to dynamically learning about routes through BGP, and the next hop is the corresponding Direct Connect gateway, which makes it easy to perceive routing changes in IDC. Currently, routes published to CCN can be controlled based on AS-PATH:
  • If the AS-PATH lengths are the same, CCN will accept all routes.
  • If the AS-PATH lengths are different, CCN will accept routes with a shorter AS-PATH.

• Dynamic learning (BGP) is in beta test. If you want to use it, please submit a ticket for application.
• AS-PATH description:
  i. The information of AS-PATH can be viewed in the Direct Connect gateway.
  ii. 32-bit string is supported. If the string is exceptional, the route will be deleted, and a string exception event will be reported, for which you can configure event alarming.
  iii. The maximum AS-PATH length is 30; if the maximum length is exceeded, the AS-PATH will be truncated, and a truncation event will be reported, for which you can configure event alarming.
  iv. Three AS numbers (45090, 139341, and 45090) will be added to the AS-PATH that passes through Direct Connect gateway - CCN - Direct Connect gateway.

2. During addition

• Check policy: if it overlaps any existing route, routes newly added will become invalid by default to avoid affecting existing routes. You can adjust their validity after assessing the impact.
• No-check policy: all routes will be valid except ECMP routes. For more information, please see the routing logic in same IP ranges in section 3 below.

  The no-check policy feature is in beta test. If you want to use it, please submit a ticket for application.

3. After addition

• Different overlapping IP ranges: based on the longest mask matching rule, a more specific IP range will have a higher priority.
• Same IP ranges: routes whose next hops are all Direct Connect gateway support ECMP, which is not supported in other cases (i.e., routes cannot be set to valid at the same time); for example, the next hops of the routes are all VPC or VPC and Direct Connect gateway.

Automatic Route Deletion